Does the battery connector from the gun actually lead out through to the handguard area? Pics look like there's plenty of room for a mini in the buffer tube.

It comes with a hi-cap mag. Unless it's similar in design to the TM M4 hi-caps that can unload a full mag on one full proper wind, you'll find you're going to have to tickle it occasionally to keep it feeding properly. That isn't uncommon.

the barrel blocks most of the battery then when I reapply the bottom handguard it does not fit.